1. Field of the Invention
The present invention relates to a vehicular remote door lock controller that is suitable for use in a smart entry system for unlocking the doors of a vehicle according to a bidirectional authentication process that is performed with a vehicle-mounted unit (vehicle-side controller) when the owner (user) of a portable unit touches an outer door handle, which functions as a touch sensor, of the vehicle, or a smart entry system for unlocking the doors of a vehicle free of touch sensors according to a bidirectional authentication process between a vehicle-mounted unit (vehicle-side controller) and a portable unit, that automatically starts when the owner of a portable unit approaches the vehicle.
2. Description of the Related Art
In recent years, there have been proposed various remote door lock controllers for locking and unlocking vehicle doors with a radio signal transmission/reception portable unit without inserting a key into a key cylinder, to be used as a substitute for or in combination with conventional vehicular door lock devices which lock and unlock vehicle doors by inserting a key into a key cylinder.
The proposed remote door lock controllers use radio signals in an LF (Low Frequency) range (30 through 300 [kHz]), e.g., radio signals having frequencies of 125 [kHz] or 134 [kHz], for mutual radio communications between the vehicle and the portable unit.
Radio signals in the above LF range cover distances, according to output level, that are shorter than distances by radio signals used by remote door lock controllers in VHF/UHF bands including a frequency of 300 [MHz]. Usually, antennas are installed on the vehicle near the doors thereof for sending radio signals in the above LF range.
FIGS. 15A and 15B of the accompanying drawings show a layout of vehicular LF antennas 6a through 6e installed on respective doors 4a through 4e of a vehicle 2 which incorporates a conventional vehicular remote door lock controller 8.
In FIGS. 15A and 15B, the doors 4a, 4c are doors near a driver seat and a front passenger seat, respectively, the doors 4b, 4d are doors near rear passenger seats, respectively, and the door 4e is a trunk door or a hatchback door.
In order for the vehicular remote door lock controller 8 to detect a portable unit which may be present in areas around the doors 4a through 4e of the vehicle 2, the antennas 6a through 6e send respective request signals Ra through Re successively at times t1 through t5 for respective constant periods tα, as indicated by a timing chart shown in FIG. 16 of the accompanying drawings.
FIG. 15B shows effective transmission ranges (communication ranges) 10a through 10e of the respective antennas 6a through 6e for the request signals Ra through Re.
If a portable unit is present in either one of the effective transmission ranges 10a through 10e of the respective antennas 6a through 6e, then the portable unit which has received one of the request signals Ra through Re sends a response signal to a control unit of the vehicle 2. In response to the response signal, the control unit locks and unlocks the doors 4a through 4e. 
The vehicular remote door lock controller 8 shown in FIGS. 15A and 15B which locks and unlocks the doors without inserting a key into a key cylinder is disadvantageous in that since the antennas 6a through 6e need to be installed in the vicinity of the doors 4a through 4e, respectively, the number of antennas used is large, making the vehicular remote door lock controller 8 costly and heavy.
Furthermore, inasmuch as the five antennas 6a through 6e successively transmit request signals, it takes time to detect a portable unit that may be positioned in the effective transmission ranges.
Conventional arrangements as to a layout of antennas and a process of sending signals from antennas are disclosed in Japanese Laid-Open Patent Publications Nos. 60-159264 and 2002-46541.
Specifically, Japanese Laid-Open Patent Publication No. 60-159264 shows a pair of loop antennas mounted on a rear portion of a vehicle, e.g., rear combination lamps, rear finishers, a rear bumper, or a rear window glass pane. The loop antennas simultaneously transmit request signals to detect a portable unit for locking and unlocking the trunk door of the vehicle.
Japanese Laid-Open Patent Publication No. 2002-46541 reveals a technique having antennas disposed centrally on front and rear seats, respectively, in the passenger compartment of a vehicle for simultaneously transmitting signals to detect a portable unit while reducing a non-communication range within the passenger compartment based on an overlap of radio waves, and also a technique having four antennas disposed respectively on front and rear portions of the left and right sides of a vehicle for simultaneously transmitting signals to provide a constriction-free communication range outside of the passenger compartment to detect a portable unit.
The arrangement disclosed in Japanese Laid-Open Patent Publication No. 60-159264 resides in that since the directivity of the antenna of the portable unit is unidirectional, the loop antennas simultaneously transmit radio signals that are out of phase with each other by 90°. Therefore, regardless of which direction the directivity of the antenna of the portable unit is oriented in, the portable unit can be detected to lock and unlock the trunk door of the vehicle. However, the number of antennas used on the vehicle is increased rather than reduced, and the publication discloses nothing about efforts to reduce the number of antennas used on the vehicle.
The techniques disclosed in Japanese Laid-Open Patent Publication No. 2002-46541 for simultaneously energizing the antennas on the front and rear portions of the vehicle to provide a constriction-free communication range outside of the passenger compartment are illustrated in the drawings. However, nothing is disclosed in the publication about efforts to reduce the number of antennas used on the vehicle.